Militants from a breakaway al-Qaida group extended their control over a swath of Iraq, advancing toward Baghdad after capturing the birthplace of Saddam Hussein, as the U.S. continued to weigh an Iraqi request for air strikes.

After seizing Mosul, Iraq’s second-biggest city, fighters from the Islamic State in Iraq and the Levant moved yesterday into Saddam’s hometown of Tikrit, about 80 miles (130 kilometers) north of Baghdad, Noureddin Qablan, vice chairman of the Nineveh provincial council, said by phone. In Mosul, ISIL took dozens of people hostage at the Turkish consulate, as hundreds of thousands of residents fled the city.

The U.S. has yet to respond to a request from Iraq made last month to mount air attacks against militant training camps in western Iraq, according to two American officials who asked not to be identified discussing internal deliberations. One of the officials said President Barack Obama is reluctant to revisit a war that he opposed and repeatedly has declared over.

The surge in violence across northern and central Iraq, three years after U.S. troops withdrew, has raised the prospect of a return to sectarian civil war in OPEC’s second-biggest oil producer. Prime Minister Nouri al-Maliki’s Shiite-led government is struggling to retain control of Sunni-majority regions, and his army collapsed in the face of the Islamist advance.

“The threat is very significant. ISIL has huge numbers in terms of manpower and control of weapons,” said Julien Barnes- Dacey, an analyst at the European Council on Foreign Relations in London, said by phone. “It has fighting experience from Iraq and the civil war in Syria, and has gained control over large amounts of territory.”

There were conflicting reports from Baiji, a town north of Baghdad that’s home to the nation’s largest refinery. Mayor Mohammed Mahmoud said the refinery was working normally and under guard by tribesmen and police, after earlier reports that the militants were fighting to take it over. The conflict hasn’t immediately hurt Iraq’s oil exports, though it halted repair work on an export pipeline.

The U.S., which invaded Iraq in 2003 and kept troops there until 2011, condemned the attacks by ISIL and offered its commitment to support the Iraqi government’s fight against the militants, according to a White House statement. The Obama administration is prepared to increase, as needed, assistance to Iraq combat the militants, according to the statement.

The U.S. is weighing options including expedited equipment and training for the Iraqi military, according to a White House official who also asked not to be identified. Some money may eventually come from a $5 billion fund that Obama has asked Congress to approve to help U.S. allies fight terrorism.

Maliki pledged again yesterday to take swift action to recapture Mosul, and said he’ll bolster Iraq’s regular forces with volunteers.

More than 150,000 troops fled their posts in Mosul and surrounding areas, leaving behind thousands of weapons, as well as tanks and helicopters, that are now in ISIL’s possession, said Jabbar Yawer, a spokesman for ethnic Kurdish armed forces in Erbil.

The Kurdish authorities who control that part of northern Iraq have deployed more of their Peshmerga fighters to fortify defensive positions, Yawer said in a phone interview. Kirkuk, the biggest northern oil field, is under the control of the Peshmerga and “the situation is calm” there, he said.

About 500,000 civilians fled Mosul, 80 miles from the borders with Turkey and Syria, and surrounding areas, according to the International Organization for Migration. Yawer said tens of thousands of families were headed to Kurdish-controlled areas.

ISIL also is among the mostly Sunni groups fighting to topple Syria’s President Bashar Assad. It established semi-permanent encampments in desert areas of western Iraq, especially in Anbar and Nineveh provinces, to provide secure bases for its fighters in Syria, the U.S. State Department said in an April report.

Now it’s showing its strength in Iraq and “will probably succeed in expanding the territory it controls in Iraq’s predominantly Sunni northern provinces” in the next six months, research firm IHS said in an e-mailed report.

In a televised speech, Maliki said ISIL won’t be allowed to stay in Mosul, adding that government forces were much stronger than the militants. Maliki, who has called for a state of emergency in areas affected by the violence, also said commanders who fled must be punished.

Maliki’s call on Shiite militias to help against ISIL was answered by Moqtada al-Sadr, a cleric whose fighters played a key part in the civil war that flared up in 2006. Al-Sadr said he’s ready to “coordinate with some government entities” and set up brigades to “defend things that are sacred,” according to the Al-Mada news agency.

The fighting in Mosul has halted repair work on the main oil pipeline to Turkey, state-run North Oil Co. said. Shipments through the Kirkuk-Ceyhan pipeline, the target of frequent attacks, have been stopped since March 2.

Iraq produced 3.3 million barrels of oil a day in May, making it the second-largest producer in the Organization of Petroleum Exporting Countries after Saudi Arabia. An estimated 17 percent of the country’s oil reserves are in the north, according to the Energy Information Administration. That includes the giant Kirkuk field, in a region disputed between the Baghdad government and the Kurds.